/*
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package com.srcptit.trainning.hanhpt.btvn1;

import java.util.Scanner;

/**
 *
 * @author Administrator
 */
public class Bai5M1
{
    public static void main(String[] args) 
    {
        Scanner sc=new Scanner(System.in);
        int n= sc.nextInt();
        long [] a= new long [n+1];
        a[0]=0;
        a[1]=1;
        for(int i=2;i<=n;i++)
            a[i]=a[i-1]+a[i-2];
        System.out.println(a[n]);
        
    }
}
